Validation of time-variable gravity field products with globally distributed in situ ocean bottom pressure observations
19/09/2016 | 16:30 | Session 1: Current and future satellite gravity missions
Author(s): Lea Poropat, Inga Bergmann-Wolf, Henryk Dobslaw and Frank Flechtner
Lea Poropat, Inga Bergmann-Wolf, Henryk Dobslaw and Frank Flechtner
Time variable global gravity field models that are processed by different research institutions all across Europe are currently compared and possibly subsequently combined within the "European Gravity Field Service for Improved Emergency Management (EGSIEM)" project founded by the European Union. To objectively assess differences between the results from different groups, and also to evaluate the impact of changes in the data processing at an individual institution in preparation of a new data release, a validation of the final GRACE gravity fields against independent observations is required.
For such a validation, we apply data from a set of globally distributed ocean bottom pressure sensors. We identify outliers, remove instrumental drifts and trends by a quadratic fit, stack time series from re-deployments including the removal of jumps in the time series due to recovery and re-deployment of a sensor, harmonize the time sampling to one hour, and finally eliminate tidal signals using the T_TIDE MATLAB package for classical harmonic analysis. Both GRACE and in situ time-series are subsequently filtered by 3rd order Butterworth bandpass filters in order to focus on selected frequency bands only. The validation typically concentrates on seasonal to interannual signals, but in case of GRACE-based series with daily sampling available from, e.g., Kalman Smoother Solutions, also sub-monthly signal variability can be assessed.